Add vim swap files to .gitignore

Change-Id: I8db056a61e76b58ba0ca98c7b411f656c76352b6
diff --git a/.gitignore b/.gitignore
index 9703f16..b59cb77 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
+*.sw?
 *.egg
 *.egg-info
 *.pyc